1. Field of the Invention
The invention relates to apparatuses for applying glue, and more particularly to an apparatus for applying glue to a heat sensitive, moisture proof film.
2. Discussion of the Related Art
Articles, such as baby diaper pants, diaper inserts, sanitary towels, patient underlays and operation dressings, which serve for absorbing fluid secreted from the body generally have on one side a fluid-impermeable, highly pliable film of small thickness, such as polypropylene, onto which is glued an absorbent surface pad composed of cellulose or a suitable plastic and covered by a nonwoven fleece-like material.
The absorbent pad is composed of a short-fiber wad of loose material which must be secured to the film, so that it maintains its position and does not slip during the handling of the article. Therefore, the absorbent pad must be adhesively bonded to the film.
This adhesive bonding process is difficult because the film which receives the glue is highly sensitive both mechanically and thermally. Prior attempts have been made to carry out the adhesive bonding by means of cold glue. However, cold glue is an aqueous dispersion, and, therefore, there may be problems with the possible inclusion of moisture when an absolutely leakproof final pack is desired.
The alternative is to use a hot-melt adhesive, but with this there are difficulties in achieving a uniform distribution of a small coating quantity over the coating width which is generally in the range of 200 to 800 mm. When coating is carried out with a single coating nozzle continuous over the coating width, considerable effort is involved in making the small quantity of glue flow out of the nozzle slit uniformly. In particular, a distribution which is to some extent uniform requires a low viscosity hot-melt adhesive which is applied at temperatures in the range of 110.degree. to 140.degree. C. Even under these conditions, the uniformity is unsatisfactory. The high temperature of the applied glue and the coating quantity (about 2-4 g/m.sup.2), lead to a pronounced deformation of the film and irregular corrugations on the rear side of the hygiene article produced.
A further prior process comprises applying onto the film only individual narrow glue tracks laid next to one another at intervals. However, these glue tracks are likewise clearly pronounced on the rear side of the film. Also, between the glue tracks channels are formed, in which the absorbent pad is not connected to the film and through which fluid can escape.